1. Field of the Invention
This invention relates to a process for the preparation of 3-pentenoic acid by reacting butadiene with carbon monoxide and water in the presence of a rhodium-containing catalyst and an iodide promoter. More specifically but not by way of limitation, the invention relates to an improved method of isolating and recovering 3-pentenoic acid involving the use of carbon monoxide to vaporize the 3-pentenoic acid.
2. Description of the Prior Art
Numerous patents address the hydrocarboxylation of butadiene to 3-pentenoic acid. U.S. Pat. No. 5,250,726 details the reaction of butadiene with carbon monoxide and water in a carboxylic acid solvent in the presence of a rhodium catalyst, an iodide promoter, and a sulphonic acid catalyst. U.S. Pat. No. 5,145,995 claims a process which reacts butadiene with carbon monoxide and water in a carboxylic acid solvent in the presence of rhodium and an iodide or bromide promoter. U.S. Pat. No. 4,622,423 discloses a process for the preparation of 3-pentenoic acid by hydrocarboxylating butadiene with carbon monoxide and water in the presence of a rhodium-containing catalyst, an iodide promoter and certain inert halocarbon solvents. U.S. Pat. No. 4,690,912 claims a catalyst system for carboxylation reactions which consists of rhodium and an iodide containing promoter.
U.S. Pat. No. 5,227,520 discloses a process for purifying an iodide-contaminated carboxylic acid product from an iodide promoted carboxylation which comprises vaporizing the carboxylic acid to free it of catalyst, feedstock, and promoter wherein the vaporized carboxylic acid has a reduced iodide contamination.
U.S. Pat. No. 5,237,097 claims a carbonylation process where the product solution is conveyed to a separation zone where in the presence of carbon monoxide, the product is distilled. In the process, the absolute temperature and pressure in the separation zone is lower than in the reaction zone.
PCT Application WO96/14287 discloses a process for preparing carboxylic acids where following reaction the product is separated from the catalyst by vaporization. Following separation, the non-volatilized portion is placed in contact with carbon monoxide prior to being returned to the reaction zone. The exposure to carbon monoxide is done in a manner which does not allow carbon monoxide to return to the separation zone.